The distribution of species along coastlines can be regarded as approximately one dimensional, that is, linear along the coast with little breadth of distribution. In practice, this significantly enhances the application of museum records to questions about species' ranges. In particular, the records can demonstrate range reductions given reasonable provenance accuracy, and adequate contemporary surveys. This approach has been used to reveal a range reduction in the mussel Brachidontes rostratus, whose distribution characterises the Peronian-Maugean boundary. This reduction is a warning that many other species whose northern range ends at this boundary are at risk of being lost from New South Wales as a result of climate change.